Molded fiber reinforced plastic leaf spring

ABSTRACT

A molded fiber reinforced plastic leaf spring. The spring has a curved central section composed of longitudinally extending fibrous strands impregnated with a cured thermosetting resin. The central section is generally rectangular in cross section having rounded upper and lower edges and a ground-off parting line disposed substantially at the neutral axis of the spring.

This application is a continuation of application Ser. No. 06/791,569filed Oct. 25, 1985, now abandoned,which application is a division ofapplication Ser. No. 06/543,354 filed Oct. 19, 1983, now U.S. Pat. No.4,560,525.

BACKGROUND OF THE INVENTION

There has recently been considerable activity in the production of fiberreinforced plastic leaf springs for vehicles due to the substantialreduction in weight as compared to metal leaf springs. Fiber reinforcedplastic leaf springs can be produced by winding fibrous strandsimpregnated with a thermosetting resin around a pair of spaced bushings.After the desired number of windings have been made to produce therequired strength characteristics, the wound structure is placed in amold and the thermosetting resin is cured. The resulting cured productconsists of a generally curved central section and integrally connectedend portions having openings or eyes adapted to receive connectingmembers.

In other methods of manufacture, the curved central section of the leafspring is molded separately from resin-impregnated fibrous material, andafter molding, the ends of the central section are mechanicallyconnected to metal end members having openings to receive connectorsthat connect the spring to a vehicle.

It is desired that the curved central section of the spring haverounded, longitudinal edges because sharp edges tend to produce highstress areas. Rounded bottom edges can readily be produced in the moldedstructure by utilizing rounded corners for the female mold. However, inthe past rounded upper edges have not been satisfactorily produced bymolding. Grinding away the molded sharp upper edges acts to remove andsever the reinforcing fibers which reduces the strength characteristicsof the spring.

In any molding operation flash is produced at the parting line betweenthe male and female molds. When molding a fiber reinforced plastic leafspring, some fibers are carried into the flash and after molding, onremoval of the flash, these fibers are ground away. If the flash islocated at the upper portion of the spring, which is a high stress area,the removal of the flash and severing of the fibers at this location canadversely effect the physical properties of the spring. Furthermore thesevered fibers tend to produce sharp needle-like projections which canbe a hazard to handling of the spring.

SUMMARY OF THE INVENTION

The invention is directed to a molded fiber reinforced plastic leafspring. The spring is composed of a curved central section, and endsections are integrally connected to the ends of the central section andhave openings to receive connectors for attachment to the vehicle.

The curved central section is generally rectangular in cross sectionhaving opposed upper and lower surfaces connected by side surfaces, andthe longitudinal edges joining the side surfaces to the upper and lowersurfaces are rounded or curved.

The ground off flash at the parting line is located substantially at theneutral axis of the central action in a low stress area, so that anysevering of fibrous materials on removal of the flash will not adverselyeffect the physical characteristics of the spring.

In accordance with the method of the invention, the curved centralsection of the spring is molded in a mold assembly consisting of afemale mold and a cooperating male mold. The female mold includes abottom wall and side walls which are connected to the bottom wall byrounded corners, while the male mold is composed of an upper wall andside walls which extend downwardly and are received within the sidewalls of the female mold. The side walls of the male mold are connectedto the upper wall by rounded corners and the lower extremities of theside walls of the male mold terminate in generally flat surfaces.

In the molding operation, the wound fibrous structure impregnated withthe uncured thermosetting resin is placed in the female mold and themolds are then moved relative to each other to bring the male mold intoregistry with the female mold. Sufficient compressive force is appliedto the male mold to bring the lower extremities of the side walls of themale mold to a point on the neutral axis of the spring. During themolding, the liquid resin and fibrous reinforcement may be squeezed outalong the parting line between the side walls of the male mold and theadjacent side walls of the female mold to produce flash. As the flash islocated on the neutral axis of the spring, the subsequent removal of theflash, after the molding operation, and severing of the fibrous materialwill not adversely effect the physical properties of the spring.

The resulting molded leaf spring has rounded upper and lowerlongitudinal edges, obtained without machining or grinding, whichreduces the stress concentrations at the edges. Because of this, thespring has better physical properties per unit weight than prior artfiber reinforced plastic leaf springs.

Other objects and advantages will appear in the course of the followingdescription.

DESCRIPTION OF THE DRAWINGS

The drawings illustrate the best mode presently contemplated of carryingout the invention.

In the drawings:

FIG. 1 is a perspective view of a fiber reinforced plastic leaf springas produced by the invention;

FIG. 2 is a schematic view showing a method of winding the leaf springprior to molding;

FIG. 3 is a section taken along line 3--3 of FIG. 1;

FIG. 4 is a transverse section of the mold assembly for molding thecurved central section of the leaf spring; and

FIG. 5 is a fragmentary enlargment of the structure shown in FIG. 4.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENT

FIG. 1 illustrates a fiber reinforced plastic leaf spring 1 to be usedfor a vehicle and composed of a curved central leaf section 2 and endsections 3. Each end section 3 is provided with a metal or plasticbushing 4 having an opening to receive a connecting member to attach thespring to a vehicle in the conventional manner.

The central section 2 and end sections 3 are preferably composed ofsubstantially continuous windings of fibrous material impregnated with acured thermosetting resin. The fibrous reinforcement can take the formof mineral fibers, such as glass; vegetable fibers, such as cotton;animal fibers such as wool; synthetic fibers such as nylon, Dacron, orOrlon; or metal fibers, such as steel wire.

The thermosetting resin can be any conventional thermosetting resin,such as an epoxy or polyester resin, used in forming fiber reinforcedresin products.

As shown in FIG. 3, the central section 2 is generally rectangular incross section, having an upper surface 5 and a lower surface 6 connectedby side surfaces 7. The longitudinal edges 8 connecting the uppersurface 5 and side surfaces 7, as well as the longitudinal edges 9connecting lower surface 6 and side surfaces 7, are generally curved orrounded which tends to reduce stress concentrations at these areas.

In addition, longitudinal ribs 10 extend outwardly from each sidesurface 7 and ribs 10 have flat upper surfaces 12 that lie generallyalong the neutral axis 13 of the spring. In the lower stress areas ofcentral section 2, adjacent end sections 3, ribs 10 are less prominentand merge into the end sections.

FIG. 2 illustrates schematically a manner of winding leaf spring 1 fromcontinuous strands or rovings 14 of fibers impregnated with the uncuredresin. In this method, the strands 14 are wound helically around thespaced bushings 4. When the desired number of layers are wound to obtainthe required physical properties in the spring, the wound structure,with the tension relaxed, is placed in a mold assembly 15, with the tworuns 16 and 17 of the wound structure falling together in the bottom ofthe cavity 18, in the female mold 19.

The mold assembly 15 also includes a male mold 20 which is adapted tocooperate with the female mold 19 to mold the wound structure. As bestillustrated in FIG. 4, cavity 18 of female mold 19 is defined by abottom wall 21 and a pair of spaced side walls 22 which are joined tothe bottom wall by rounded corners 23. Each side wall 22 is providedwith a generally flat upwardly facing shoulder 24.

Male mold 20 consists of an upper wall 25 and a pair of spaceddownwardly extending side walls 26 which are received within the sidewalls 22 of the upper portion 30 of female mold 19. As illustrated inFIG. 4, the side walls 26 are connected to upper wall 25 by roundedcorners 27. The lower extremities of side walls 26 terminate in flatsurfaces 28 aligned with shoulders 24.

After the wound structure of the central section 2 is placed in thecavity 18 of the female mold 19 a predetermined force is applied to malemold 20 to compress the wound material. The predetermined force appliedto the male mold will bring the lower surfaces 28 of side walls 26 ofmale mold 20 into general alignment with the neutral axis 13 of thespring section 2. The neutral axis 13 lies midway of the height ofcentral section 2, as illustrated in FIGS. 3 and 5.

During the molding operation, a portion of the uncured resin, along withsome fiber reinforcement may be squeezed or extruded outwardly along theparting line 29 between the male and female molds. The parting line islocated at the junction between the outer surface of the side walls 26of male mold 20 and the inner surface of upper portion 30 of female mold19.

Heat is normally applied to the fiber reinforced plastic structureduring the molding operation to accelerate the cure of the thermosettingresin. Heat can be applied by placing the mold in an oven, oralternately employing a heating mechanism formed integrally with themale and female molds.

After curing of the resin, male mold 20 is removed from the cavity 18 ofthe female mold and the molded structure is removed from the femalemold. The material extruded along the parting line 29 during the moldingoperation will constitute flash which can be ground away to complete theoperation. As the flash is located along the neutral axis 13, thegrinding of the flash, and the severing of fiber reinforcement locatedin the flash, will not adversely effect the physical properties of themolded spring.

As both the male and female molds have rounded corners as indicated by23 and 27, the molded central section 2 will have rounded upper andlower longitudinal edges 8 and 9 and this reduces high stressconcentrations at these edges.

Ribs 10 are formed by cooperation of shoulders 24 and surfaces 28 duringthe molding operation. In certain instances, the shoulders 24 can beeliminated, in which case the molded product, instead of having ribsalong each side, will have upwardly facing edges or shoulders along eachside.

As the parting line between the male and female molds and the resultingflash is located substantially along the neutral axis, the removal ofthe flash and the severing of any fibrous reinforcement in the flashwill not adversely effect the physical properties of the spring. Becauseof this, the spring has improved physical properties.

Various modes of carrying out the invention are contemplated as beingwithin the scope of the following claims particulary pointing out anddistinctly claiming the subject matter which is regarded as theinvention.

I claim:
 1. A molded fiber reinforced resin leaf spring, comprising acurved central section and a pair of end sections connected to the endsof said central section with each end section defining a bushing, saidspring being composed of substantially continuous fibrous materialimpregnated with a cured thermosetting resin with said fibrous materialextending continuously through said central section and around saidbushings, said central section having opposed upper and lower surfacesconnected by side surfaces and said central section having rounded edgesconnecting the side surfaces to the respective upper and lower surfaces,said central section having a neutral axis disposed substantially midwaybetween the upper and lower surfaces, and a rib extending laterally fromeach side surface with each rib having a surface extending substantiallythe length of said central section and being located substantially atsaid neutral axis, said rib and said central section being a one-piecestructure, said fibrous material having severed extremities disposed atsaid surfaces.